The present invention relates to a booster as may be used in a brake of an automobile, and more particularly, to an improvement of a valve mechanism of a brake booster which includes a solenoid which can be energized to operate the valve mechanism.
A brake booster is known in the art comprising a valve body slidably disposed within a housing, a power piston mounted on the valve body to partition the interior of the housing into a constant pressure chamber and a variable pressure chamber, a valve mechanism mounted on the valve body to supply a fluid to or to displace it from the variable pressure chamber, an input shaft to operate the valve mechanism, and a solenoid for driving a solenoid plunger which is slidably mounted on the valve body reciprocatively to operate the valve mechanism.
A conventional brake booster as mentioned above suffers from a drawback that when a brake reaction is transmitted to the solenoid plunger as the solenoid is energized, the reaction which is transmitted to the solenoid plunger experiences a large variation in magnitude. Accordingly, there has been a difficulty in controlling a brake output with a high accuracy by controlling a current or a voltage applied to the solenoid. Accordingly, to eliminate such disadvantage, the present Applicant has previously proposed a brake booster having an improved valve mechanism in Japanese Patent Application No. 222,138/2001, as illustrated in FIG. 5 of the present Application, for example.
As shown in FIG. 5, in the cited Application No. 222,138/2001, a tubular, second vacuum valve seat member 11 is slidably mounted on a valve body 3 and a second vacuum valve seat 12 is formed on the rear end of the second vacuum valve seat member 11. When a solenoid 8 is energized, a solenoid plunger 26 drives the second vacuum valve seat member 11 rearward toward a valve element 16. In this manner, the second vacuum valve seat 12 becomes seated upon the valve element 16 before an atmosphere valve seat 14 is removed from the valve element 16, thus allowing the brake booster to be actuated without depressing a brake pedal.
However, in the brake booster proposed in the cited Application No. 222,138/2001, a core member 27 which defines a magnetic path for the solenoid 8 is fixedly mounted on the valve body 3 at a location rearward of the solenoid plunger 26 within the valve body 3. When the solenoid 8 is energized, the solenoid plunger 26 is driven rearward relative to the valve body 3 and thus, there has been a need for the provision of a clearance between the solenoid plunger 26 and the core member 27 when the brake booster is not actuated which is sufficient to avoid an abutment between the both members when the solenoid 8 is energized.
However, when a clearance is maintained between the solenoid plunger and the core member which is located rearward thereof when the brake booster is not actuated, it becomes necessary to increase the magnitude of the current which energizes the solenoid in order to move the solenoid plunger. Consequently, in the cited Application No. 222,138/2001, the solenoid increases in size, leading to an increased size of the brake booster.
In view of the foregoing, the present invention relates to a brake booster comprising a valve body slidably disposed within a housing, a power piston mounted on the valve body for partitioning the interior of the housing into a constant pressure chamber and a variable pressure chamber, a valve mechanism mounted on the valve body for supplying a fluid to or displacing it from the variable pressure chamber, an input shaft for operating the valve mechanism, and a solenoid for driving a solenoid plunger which is slidably mounted on the valve body reciprocatively to operate the valve mechanism, the valve mechanism including at least first valve means disposed in the valve body and second valve means mounted on the input shaft. In accordance with the present invention, a valve member is slidably disposed within the valve body to define the first valve means so that when the solenoid is energized, the valve member moves relative to the valve body in response to the solenoid plunger to operate the valve mechanism. A core member which forms part of a magnetic path for the solenoid is disposed at a location which opposes the direction in which the solenoid plunger is moved so as to be movable relative to the valve body and so as to allow the core member to be linked to the input shaft.
With the described arrangement of the present invention, the core member is mounted to be movable relative to the valve body and can be linked to the input shaft. Accordingly, as the solenoid plunger moves, the core member moves also. This allows the solenoid to be reduced in size, and hence the brake booster to be reduced in size as compared with the cited Application.
Above and other objects, features and advantages of the present invention will become apparent from the following detailed description of several embodiments thereof with reference to the drawings.